Embodiments of invention relates to multilevel converters and more specifically to a system and method for voltage balancing in multilevel converters.
Multilevel converters are generally used in high power industrial applications such as variable speed drive (VSD) systems or in energy conversion applications such as a solar (or photovoltaic) power generation systems, wind turbine generators and high voltage direct current (HVDC) transmission systems. One example of a multi-level converter is a flying capacitor (FC) multilevel converter. The flying capacitor multilevel converter includes a number of capacitors referred to as flying capacitors. The flying capacitors are charged to various voltage levels and by changing switching states the flying capacitors and a dc source are connected in different ways and produce various line-to-neutral output voltages.
Voltage balancing of flying capacitors is a challenge when operating the flying capacitor multilevel converter. Flying capacitors voltage unbalance (i.e., unequal voltages across flying capacitors) may overstress the capacitors and switching devices and cause over voltage and under voltage trips during the operation of the converter. Flying capacitors voltage unbalance also causes an increase in output voltage total harmonic distortion (THD) and may cause the control loop to become unstable.
One of the known solutions utilized to balance voltages of flying capacitors uses additional balancing circuitry. However, the balancing circuitry adds cost, losses, volume to the flying capacitor multilevel converter and also needs to be designed carefully.
Therefore, it is desirable to provide a method and a system that will address the foregoing issues.